1. Field of the Invention
This invention relates to a technique for automatically and selectively mounting a part onto a printed circuit board, and more particularly to a technique for automatically and selectively mounting, at a part mounting step for a printed circuit board, some parts individually onto the printed circuit board after electronic parts such as ICs or LSIs have been collectively mounted onto the printed circuit board using various part techniques.
2. Description of the Related Art
Mounting of post-mounting parts at a part mounting step for a printed circuit board is normally performed by hand. The reason is that a part already mounted acts as an obstacle or otherwise adversely affects heating involved in soldering operations, and this makes automation difficult. Such mounting by hand naturally includes a large number of operation steps and is low in efficiency, and causes an increase in personnel expenses and tends to cause incomplete soldering results.
Such an automatic soldering technique as illustrated in FIG. 20 is one of conventional well-known automatic soldering techniques used to solve the problem described above. Reference numeral 1 denotes a printed circuit board onto which post-mounting parts should be mounted, and the printed circuit board 1 is transported by a conveyor (not shown). Reference numeral 2 denotes a post-mounting part (for example, a multiple pin connector) having a plurality of lead pins 3. The post-mounting part 2 is temporarily fastened in a condition wherein the lead pins 3 thereof are inserted from above in through-holes formed in the printed circuit board 1.
Reference numeral 4 denotes a soldering nozzle. The soldering nozzle 4 has, at an upper portion thereof, an opening 5 in which all of the lead pins 3 of the post-mounting part 2 to be soldered can be inserted. Reference numeral 6 denotes a molten solder generator. Molten solder 7 is injected moderately from the opening 5 of the soldering nozzle 4 by the molten solder generator 6. The soldering nozzle 4 is moved in upward and downward directions by an elevator (not shown).
The printed circuit board 1 is transported by the conveyor to a position at which the post-mounting part 2 to be soldered corresponds to the soldering nozzle 4. Then, the soldering nozzle 4 is moved upwardly by the elevator as shown in FIG. 21A until all of the lead pins 3 of the post-mounting part 2 which project to the rear face side of the printed circuit board 1 are inserted into the opening 5 of the soldering nozzle 4. Thereafter, the soldering nozzle 4 is moved downwardly by the elevator as shown in FIG. 21B so that the lead pins 3 of the post-mounting part 2 are collectively soldered and secured to the corresponding through-holes of the printed circuit board 1.
Further, in order to ensure such good soldering results as described above, such as good wettability and so forth of the solder, application of flux, preliminary heating or some other pre-processing is required. Conventionally, the steps of application of flux, preliminary heating and soldering are performed by different apparatuses.
The prior art described above, however, has the following problems. In particular, it sometimes occurs that, as also seen from FIG. 21B, when the lead pins are drawn up from within the opening of the soldering nozzle, solder sticks across adjacent lead pins, resulting in a soldering failure, such as short-circuiting. This problem is particularly remarkable where a post-mounting part is a multiple pin connector having a plurality of lead pins or a like electric device, and it is considered that the problem arises from the fact that, since a flow of molten solder is retarded and cooled by a plurality of lead pins at a location at or around a central portion of the opening of the soldering nozzle, the viscosity of the molten solder increases at that location.
Further, according to the prior art, a soldering nozzle for exclusive use for a post-mounting part which makes an object for soldering must be used as the soldering nozzle, and this lacks in universality. Accordingly, the prior art also has a problem in that it cannot flexibly cope with a change of an object part necessitated by a change of design or the like and much time is required for an exchanging operation of the soldering nozzle.
Furthermore, since the flux application step and the preliminary heating step for assuring high wettability of solder and so forth are performed by different independent apparatuses independently of the soldering step, there is a further problem in that the entire system has a great size and requires a high cost.
Meanwhile, since a nozzle for application of flux and a preliminary heating nozzle for exclusive use for a post-mounting part which makes an object for soldering are used for the flux application step and the preliminary heating step similarly as the soldering nozzle described above, they must be replaced upon changing of the setup necessitated upon changing of the model to be manufactured. Accordingly, there is a still further problem in that, in a manufacturing line for manufacturing a small quantity each of a large number of models, much time is required for replacement or adjustment of the nozzles and manual operation is always required.